So the proper definition of a Pich-off voltage is Pinch of voltage is that 'Drain-Source' voltage after which the drain source current becomes almost constant(saturates).
And for n-channel JFET Pich-off voltage is positive. But because Vgs(off) (the gate source voltage at which there is no drain-source current) voltage is negative and by accident equal to the magnitude of the pinch off voltage. Hence: |Vgs(off)| = |Vp| the magnitude of the pinch off voltage is equal to Vgs(off).
And this is why we can say that |Vp| = |Vgs(off)| but in the same time Vp is a saturation voltage.
But the only difference is the minus sign. Because Vgs(off) is negative but Vp is positive.